1. Field of the Invention
The present invention relates to a control system for a synchronous machine, and more particularly to a control system for a synchronous machine, such as a synchronous motor or a synchronous generator, capable of detecting a magnetic pole position (a rotation angle) of a rotor of the synchronous machine without using a magnetic pole position detector.
2. Description of the Background
A control system for a synchronous machine needs a detector to detect a magnetic pole position (a rotation angle) of a rotor for controlling the drive of a synchronous machine (a synchronous motor, a synchronous generator). However, a synchronous machine driving device using such a detector has problems shown below as examples. First, the presence of a detector increases a volume of a synchronous machine using a detector, and this will impede to increase the output of a synchronous machine. Secondly, the maintenance and inspection work of a synchronous machine itself become necessary. This will make the efficiency of the maintenance and inspection worse. Thirdly, noises will be superposed on a signal line from a detector, and as a result, a detected value will be disturbed, and the control efficiency will become worse. Fourthly, a detector needs a power source for driving itself in most cases, and in addition to the power source for driving a synchronous machine, a separate power source must be provided. This will become factors for increase in a space for installing a power source, a power feed line, cost, etc.
For the reasons mentioned above, a control system for presuming a magnetic pole position without using a detector and making the drive control according to the presumed magnetic pole position is developed. This control system is called as the “Sensor-less control”.
As a control system for a synchronous machine equipped with such the sensor-less control means, one example thereof is described below. In a system for driving a synchronous machine, a changed portion of the output current generated by the PWM control and an integral time value of the output voltage generated by the PWM control are detected in synchronism with the PWM switching, and a magnetic pole position is detected according to the current/voltage equation of a synchronous machine using these detected values. (Refer to, for example, Patent Document 1)
[Patent Document 1] Patent Gazette No. 3312520
In the above-mentioned control system for a synchronous machine, it is necessary to particularly control the synchronous machine to generate the high-frequency components by the PWM control in order to presume a magnetic pole position of a synchronous machine by using the high-frequency components of the voltage and the current generated from the PWM control (described in Claims 4 and 5 of Patent Document 1). Therefore, it was a problem that the power loss and the noise are increased resulting from the high-frequency components as a result of such the control.